1. Field of the Invention
Recent developments in computer controlled automotive transmission systems and suspension systems regulate hydraulic pressure or flow rate within the system by energizing and deenergizing the solenoid of a solenoid actuated valve cyclically in response to a pulse width modulated control signal generated within the computer in response to various monitored operating conditions.
The generated control signal is typically a pulsating signal at frequencies of the order of 1 to 60 Hz, and within each cycle the solenoid is energized for a portion of the cycle and deenergized during the remainder of the cycle. By varying, under the control of the computer, the portion of time within each cycle during which the solenoid is energized, over a give time interval the percentage of time during which the valve is open is similarly varied.
In a controlled suspension system, the percentage of time during which the valve is fully open over a given time interval as compared to the time within that interval during which the valve is closed provides an effective opening or restriction in a flow path which is a corresponding percentage of the opening presented by the valve when fully opened. To regulate the pressure applied to a fluid pressure actuated clutch in a transmission system, the clutch is connected to a source of fluid under pressure when the valve is in one position and connected to a fluid sump at zero pressure when the valve is in the other position. In this arrangement, the pressure applied to the clutch will be that percentage of time the clutch is connected to the fluid pressure source multiplied by the pressure of the source.
Both types of systems require that a valve head be driven into engagement with a valve seat rapidly and firmly and, for a 60 Hz pulse width modulated control signal, at the rate of 60 engagements or closures per second for period of continuous operation of substantial time duration. This requirement, as a practical matter, dictates the employment of metal valve heads and seats to stand up under the wear. The employment of metal heads and seats in turn produces a problem in that a certain amount of noise is generated by each impact of a rapidly moving metal valve head with a stationary metal valve seat. Also, in the automotive industry, where parts are customarily purchases in large numbers, the unit price per part is of substantial concern.
The present invention is especially directed to an inexpensive and practical solution to the problems of minimizing both wear and operational noise in valves of the type discussed above.